To crank start an internal combustion engine, especially a two-stroke engine, the mixture must be enriched. For this purpose, a great many systems are known. Accordingly, a choke flap is mounted in a carburetor upstream of a throttle flap in order to increase the underpressure during crank strokes so that an intense pumping of fuel is effected and thereby the mixture is made rich. In starting devices of this kind, it is problematic that the operator must timely at least partially take the choke flap out of use during run-up of the engine so that an overrich engine and therefore a stalling of the engine associated therewith is avoided.
Japanese patent publication 62060971 discloses that the choke flap of a carburetor automatically opens with the run-up of the engine. For this purpose, the underpressure increasing in the intake channel is used. It has, however, been shown that a system of this kind works too slowly so that a stalling of the engine because of overenrichment can still not be precluded.
It is an object of the invention to provide an internal combustion engine having a starting device with which an overenrichment of the mixture is reliably avoided during the run-up of the engine.
The internal combustion engine of the invention includes a two-stroke engine and the internal combustion engine includes: an intake channel to which an air/fuel mixture is supplied in a flow direction; a carburetor for preparing the air/fuel mixture; a starting device configured in the region of the carburetor to enrich the air/fuel mixture during a starting operation of the engine; a bypass channel having a first end branching off upstream of the starting device viewed in the flow direction and having a second end opening downstream of the starting device; and, a switching valve mounted in the bypass channel and being movable from a position wherein the switching valve is essentially closed for starting the engine and, when the engine runs up, the switching valve being movable automatically into a less throttling position.
With the switchable bypass channel, it is ensured that an additional air path is enabled simultaneously with the run-up of the engine. This air path moves bypass air into the intake channel so that an overenrichment of the inducted air/fuel mixture is reliably avoided. The rapid switching of the bypass channel is achieved via a switching valve which is closed for starting the engine and, with the run-up of the engine, the switching valve switches automatically into a less throttling position so that the mixture is made lean and a continued running of the engine is ensured. Advantageously, the switching valve for opening the bypass channel is actuated by the combustion pressure in the combustion chamber of the engine because, with occurring combustion pressure, an ignition has taken place and the engine starts to run. It is especially practical to integrate the switching valve for the bypass channel into a decompression valve or to actuate the valve element of the switching valve by the switching element of the decompression valve.
The invention will now be described with reference to the drawings wherein:
The internal combustion engine 1 shown in
The air/fuel mixture, which is necessary for operation, is prepared in a mixture preparation unit which, in the embodiment shown, is a carburetor 12. The carburetor shown in
According to a feature of the invention, a bypass channel 20 is provided which includes two line sections 21 and 22. Referred to the flow direction 30 of the air/fuel mixture, the section 21 branches off upstream of the throttle flap 19 and the second line section 22 opens into the intake channel section 17 downstream of the choke flap 19. The line sections 21 and 22 are connected to each other by a switching valve 23 which is actuated when starting the engine. Preferably, the switching valve 23 is actuated by the combustion pressure in the combustion chamber 3 of the engine 1. In a special embodiment, the valve member 26 of the valve 23 is actuated by the switching element 27 of a decompression valve 24. The switching valve 23 is preferably integrated into the decompression valve 24. A seal (25, 36) separates the valve space 32 of the switching valve 23 from the interior space of the decompression valve 24 or from the ambient.
As shown in the enlarged view of
The valve member 26 of the switching valve 23 is mounted on the valve shaft 29. In the open position shown in
For starting, the decompression valve 24 is switched by depressing the valve shaft 29 into the open position so that the valve plate 28 is lifted from the valve seat and the combustion chamber is connected via a decompression opening 33 to the atmosphere. In this open position, the valve shaft 29 is latched via a spring-biased latch device 34.
In this start position of the decompression valve 24, the valve member 26 lies in the position 26′ shown in phantom outline in
Most internal combustion engines 1 are manually crank started, for example, via a pull-rope starter or the like which engages the crankshaft 11. The start is facilitated because of the switched decompression valve 24. As soon as an ignition is triggered via the spark plug 35, the pressure in the combustion chamber 3 increases tremendously and acts on the valve plate 28 so that the latch device 34 releases because of the pressure force and the decompression valve 24, supported by the force of the spring 31, switches into the closed position shown in
The embodiment of
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
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102 43 167.1 | Sep 2002 | DE | national |